Measuring the Passing of the Seasons in Ancient Egypt

The Nile was the source of civilization in ancient Egypt. At the edge of the Sahara desert, without the annual flooding of the Nile agriculture would have been near impossible and the cities of Egypt would have withered away.

In order to better keep track of the flooding of the Nile, the first calendars were developed in Egypt. These calendars were based on the passing of the seasons and thus the length of time it takes for the Earth to revolve around the Sun. For this reason we call this type of calendar a solar calendar.

Egypt was the only culture of its day to develop a purely solar calendar. Other developing civilizations used the moon as the basis of its calendar development, with the month as its primary measuring instrument, although they did make some changes to make months match up with the solar year. Not all did, in fact many calendars today, most notably the Islamic calendar, follow the lunar cycle and do not match up to the solar year.

The moon was not important to the ancient Egyptians. The accurate prediction of the flooding of the Nile was their primary concern, and thus they developed a 365 day year.

The Roman Calendar

The Romans inherited the calendrical system of the Egyptians, and followed a 365 day solar year. They separated the year into 12 months, which would have either 29 or 31 days. Months with special holy days would have 31 (such as Martius or Quintilis), other months would have 29.

It is from the Romans that we get many of the names of our calendar. The word calendar in fact comes from the Romans. Kalends was the 1st day of the month in Roman reckoning. Nones was the 5th or 7th day of the month, and Ides was the 13th or 15th. (Nones and Ides would change depending on whether it was a 29 day month or a 31 day month). The system of keeping track of the months and the years became known as a calendar after Kalends.

The names of the months also come from the Roman calendar. The Romans began their year in March, and the original names of the months were:

• Martius Named for Mars, the god of war.
• Aprilis Coming from aperire, which means “to open” in Latin, signifying the blossoming of the flowers and the beginning of spring.
• Maius Named for the goddess of fertility.
• Junius Named for the goddess of the moon.
• Quintillus 5 in Latin, for the 5th month.
• Sextilus 6 in Latin, the 6th month.
• September 7 in Latin, the 7th month.
• October 8 in Latin, the 8th month.
• November 9 in Latin, the 9th month.
• December 10 in Lation, the 10th month.
• Januarius Named for the god of gateways.
• Februarius A festival of purification.

Two of these months would famously change names during the reigns of the first two Emperors of Rome, where Quintillus and Sextilus would become July and August. Both of these months have 31 days, because having 31 days signified there was a holy day during that month. (One to honor Julius Caesar, and the other to honor Augustus Caesar).

The Julian Calendar

Besides the changes of the names of the month, Julius Caesar also enacted several other important changes to the calendar. The Roman calendar only had 355 days in its year. The solar year has 365.242 days. In attempt to correct the calendar and keep it in line with the seasons, the Romans would have an extra month every other year of 22 or 23 days.

The plan worked somewhat, but it actually ended up making the Roman year longer than the solar year on average by about 1 day. Julius Caesar decided to end this system, and commissioned a Greek astronomer, Sosigenes, to reform the calendar.

The reform proposed was what we now refer to as leap year. Sosigenes had determined that the solar year was actually about 365.25 days long. The length of the months would be changed so that the year lasted 365 days. Every fourth year an extra day would be added at the end of February, to make up for the loss of the quarter day between the Roman calendar and the seasons.

Julius Caesar was pleased with this development, and decided to immediately implement the new calendar. However, there was a problem. The Roman calendar was already so out of line with the seasons, that they would have to add extra days to make up for lost time. In 46 BCE, Caesar added two months totaling 67 days between November and December. That year had already seen one of the short months of 23 days after February, resulting in a year that lasted a total of 445 days.

This year of correction completed, the Julian Calendar went into effect. It would be the standard calendar in Europe until the 16th century and the time of Pope Gregory VIII.

The Gregorian Calendar

Although the most accurate calendar to that date, the Julian calendar was not perfect. The length of a solar year is not actually 365.25 days, it is 365.242 days. The difference is small, but over the years this would add up. Within a thousand years the calendar would be 7 days off the proper solar reckoning.

This bothered Pope Gregory VIII. The central celebration of Christianity is Easter, the day when Jesus rose from the dead. In 325 at the Council of Nicea it had been determined that the date of the celebration of Easter would be based upon the vernal equinox.

However, with the days shifting, the vernal equinox was moving further and further away from the time when Easter should be celebrated. The vernal equinox was by Gregory’s time over a week before the celebration, if not more.

This was a problem, and a reform was needed. The leap year system would remain intact, however 3 leap years out of every 400 years would be skipped. Every centennial year ending in 00 except for ones divisible by 400. Thus 2000 was a leap year, although 2100 will not be.

Like Julius Caesar, Pope Gregory VIII had to correct the calendar as well. He did this by skipping over 10 days in October in the year 1582. All of Europe went along with this change except England. England had just recently split with the Papacy during the reign of Henry VIII, and it was decided that England would remain on the old calendar. Thus the dates in England were always 10 days different than those in the rest of Europe until the finally went along with the reform themselves in 1751.

It is this calendar, developed by Pope Gregory VIII, which we still follow today. It is the most accurate calendar in history, although it still has its inaccuracies. Firstly, our calendar years still do not match up perfectly with the revolution around the Sun. However, it will make no significant difference for thousands of years, not even of a day.

Part of the problem is that the Earth itself is slowing down in its rotation. Every day that passes is .00000002 seconds longer than the day previous. While this is not a significant difference, it does add up, and could cause calendrical problems further down the line. However this is something that no one will need to worry about for thousands of years.

The Start of the Calendar

In the days of ancient Rome, it was traditional to date the year in relationship with the original the mythological founding of the city. In relationship with our current calendar, this would have been about 753 BCE.

Roman dating was written by giving the year since the founding of Rome. For example, in the year 1 CE, the Romans would have dated it 754 AUC (ab urbe condita; since the founding of the city).

In the early years of Christianity, this dating system continued to be used. Later on years would be counted from the end of the reign of the Roman Emperor Diocletian. This would last until the 6th century CE, when a monk by the name of Dionysus Exegesis (‘Dennis the Little’ as he is known in English lore) set out to date the birth of Jesus Christ.

By moving backwards from Diocletian’s reign, he placed the birth of Jesus at December 25th, 753 AUC. This day, then, would be the beginning of the year 1 AD (Anno Domini, the Year of our Lord). (In Medieval times New Year’s and Christmas were the same, it would not change until much later.)

The new dating system developed by Dionysus did not immediately come into effect throughout Christendom. In fact it would take several centuries for its use to become completely standardized throughout the western Christian world. Today, however, his dating is the standard for the calendar’s of much of the world, although we now know he was inaccurate. (Jesus could not have been born after 4 BCE). We also use BCE (Before the Common Era) and CE (Common Era) in place of using the traditional BC and AD.

The calendar has a long and interesting history, and even today there is talk of changing it. Movements exist, for example, to replace our calendar with a 13 month year that would make every month be of equal days, with a special World Holiday at the end of the year. There are other changes which people wish to make as well. In the future we might follow a calendar very different than the one we have now, but for the moment it seems that the Gregorian calendar is here to stay.